Bacteria feeding on Arctic algae blooms can seed clouds, affect climate

Arctic Ocean currents and storms are moving bacteria from ocean algae blooms into the atmosphere, where the particles help clouds form, according to new Colorado State University research. These biological particles can affect weather patterns throughout the world.

Particles suspended in air, called aerosols, can sometimes accelerate formation of ice crystals in clouds, which have an impact on climate and weather patterns. Such ice-nucleating particles include dust, smoke, pollen, fungi and bacteria.

“These special types of aerosols can actually ‘seed’ clouds, kind of similar to how a seed would grow a plant,” said study lead author Jessie Creamean, a research scientist in CSU’s Department of Atmospheric Science. “Some of these seeds are really efficient at forming cloud ice crystals.”

The study, co-authored by senior research scientist Paul DeMott, was recently published in the American Geophysical Union journal Geophysical Research Letters and involved field research in the Bering Strait.

Previous research had shown marine bacteria were seeding clouds in the Arctic, but how they got from the ocean to the clouds was a mystery. According to the new study, oceanic currents and weather systems brought bacteria feeding off algae blooms to the sea spray above the ocean’s surface, helping to feed the clouds.

Understanding how clouds are seeded can help scientists understand Arctic weather patterns.

How particles seed clouds

Pure water droplets in clouds don’t freeze until roughly minus 40 degrees Fahrenheit. They are supercooled below their freezing point but still liquid. Aerosols raise the base freezing temperature in supercooled clouds to 23 degrees Fahrenheit, by providing a surface for water to crystalize on, and creating clouds mixed with supercooled droplets and ice crystals. Mixed clouds are the most common type of clouds on the planet, and the best for producing rain or snow.

“Cloud seeds,” like the bacteria found in algae blooms, can create more clouds with varying amounts of ice and water. An increase in clouds can affect how much heat is trapped in the atmosphere, which can influence climate. The clouds’ composition can affect the Arctic’s water cycle, changing the amount of rain and snow that is produced. Increasing the number of clouds and changing the composition of Arctic clouds also affects northern weather systems, potentially influencing weather trends worldwide, according to the authors of the new study.

From ocean to atmosphere

To learn how biological “cloud seeds” travel from ocean depths to the atmosphere, Creamean and colleagues took samples from 26 feet (8 meters) below the water’s surface, and air samples roughly 66 feet (20 meters) above the water’s surface in the Bering Strait during an algae bloom.

Algae blooms are big increases in photosynthetic plant-like microorganisms that many ocean animals eat, including some kinds of bacteria. The researchers found bacteria known to seed clouds at the bottom of a phytoplankton bloom in the Bering Strait, but not in the surrounding air. The scientists found the same bacteria roughly 155 miles (250 kilometers) northwest of the bloom, suggesting a strong current transported the bacteria to a new spot. The bacteria were also in the air above the water. A storm brought the bacteria from the ocean depths to the surface, transporting the bacterial “cloud seeds” into the air in water droplets.

“What existed at the bottom of the ocean was making its way up to the surface waters,” Creamean said.

Since the scientists only were able to take samples from 66 feet up, they don’t yet know how the ice nucleating particles ascend to cloud elevation, which on average starts at 1.2 miles (1.9 kilometers) above the surface.

The Earth’s polar regions are experiencing rapid warming from climate change. The Arctic’s accelerated warming could cause more algae blooms as well as more bacteria of the type found to seed clouds, in turn further affecting its weather systems, according to the authors.

“This is a piece of the puzzle as to how these clouds form in the Arctic and potentially impact weather patterns all over the world,” Creamean said.

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